Both piezoceramic devices and magnetostrictive devices are known to be useful as solid state actuators or electromechanical transducers which can produce mechanical motion or force in response to a driving electrical signal. These devices have been used, for example, to generate vibrations, i.e. acoustic waves, in pipes as a means of telemetering information. Such transducers are used in drilling operations to send information from down hole instruments to surface receivers. The down hole instruments generally produce an electrical waveform which drives the electromechanical transducer. The transducer generates acoustic waves in a drill pipe which travel up the drill pipe and are detected at the surface. The detected acoustic signals are converted back to electrical signals by electromechanical transducers such as accelerometers or which may be essentially identical to the devices which transmitted the signals. The detected electrical signals are decoded to recover the information produced by the down hole instruments.
The power available from down hole instruments to drive the signal transducers is limited, since they are normally battery powered. It is important that the driving signal be efficiently converted to acoustic signals in the drill pipe. However, piezoceramic transducers are highly capacitive. In similar fashion, magnetostrictive transducers are hightly inductive. These reactive characteristics reduce the transduction efficiency, i.e. the ability to convert electrical power into acoustic power, of the telemetry system.
The capacitive nature of the piezoceramic transducers has required design of driving circuits which can drive capacitive loads or the use of an inductor with the transducer to reduce effective reactance. Likewise, the inductive nature of magnetostrictive transducers has required design of driving circuits which can drive inductive loads or the use of a capacitor with the transducer to reduce effective reactance.
It would be desirable to provide an electromechanical transducer which allows more efficient conversion of electrical power into acoustic signals.